If we want to say, when we tell a story, that two persons (including me) were part of an event. Should we say whether "At the beginning, we were two in the adventure" or "At the beginning, there were two of us in the adventure" ?
Either way is fine. "We were two" is more literary, like you are characters in a classic tale. For example:
The Musketeers were three, before D'Artagnan entered the story.
You could simply say, "There were three Musketeers at the start of the story," but sometimes you want to make it sound more dramatic. Or ominous:
Six of us began the adventure, but only I finished it.
We were six at the start of my tale, but only I remain to tell it.